Contrast enhancement layer compositions, alkylnitrones, and use

ABSTRACT

Contrast enhancement compositions are provided which can be used to make contrast enhancement layer photoresist composites. The composites can be used to make patterned photoresists under mid-UV light and utilize photobleachable alkylnitrones.

"This is a divisional of copending application(s) Ser. No. 07/445,914filed on Dec. 4, 1989, now U.S. Pat. No. 5,002,993".

BACKGROUND OF THE INVENTION

Prior to the present invention as shown by the copending application ofGriffing et al., Ser. No. 675,915, filed Nov. 28, 1984, for SPINCASTABLE PHOTOBLEACHABLE LAYER FORMING COMPOSITIONS, assigned to thesame assignee as the present invention and incorporated herein byreference, diarylnitrones were utilized in combination with inertorganic polymer binders to make contrast enhancement layer-formingcompositions. Although the diarylnitrone photobleachable layer-formingcompositions of Griffing, et al. have been found to be valuablematerials for use in near UV (350-450 nm) contrast enhanced lithography,recent interest has developed in developing photoresists for use in themid-UV imaging areas such as 300-350 nm. It has been found that,although arylnitrones can be totally bleached under mid-UV light, thediaryloxaziridines are somewhat absorbant towards mid-UV light andundergo secondary photochemical reactions. As a result,diarylnitrone-based contrast enhancing formulations are generally usedin near-UV photolithography. For example, simple diarylnitrones such asα, N-diphenylnitrone (λ313 nm, ε=22,000 L/mole cm), orα-anisyl-N-phenylnitrone (λ329 nm, ε=23,000 L/mole cm) absorb in thedesired regions and also appear to bleach efficiently in dilutesolutions. However, when cast in films of a copolymer such as styreneand allyl alcohol, the films exhibit poor bleaching characteristics.Thus, the films initially bleach rapidly, but after reaching atransmission maximum of 60% or less, transmission can fall off rapidlyif photolysis is continued. One possible explanation is that theabsorption spectrum of the oxaziridine photoproduct tails sufficientlyinto the 300 nm region to undergo secondary photochemical reactions. Itis desirable, therefore, to find nitrone systems having suitablespectral characteristics which do not undergo secondary reactions underthe applied illumination conditions.

The present invention is based on our discovery thatα-aryl-N-alkylnitrones and dialkylnitrones, as defined hereinafter,possess spectral and photochemical properties which make themparticularly well suited for use as contrast enhancement materials formid-UV (300-365 nm) applications. It has been further found that whenthese alkylnitrones are formulated with certain inert organic polymersin the presence of a solvent such as water, a water soluble organicsolvent, a mixture of water and such water soluble organic solvent, or awater immiscible organic solvent, spin castable mixtures can be madewhich are suitable for forming in situ, a photobleachable contrastenhancement layer (CEL) on the surface of a photoresist. It has beenfurther found that a suitable organic solvent can be used to strip thephotobleached (CEL) from the photoresist surface when a water insolubleinert organic polymer is used in the spin castable mixture.Alternatively, total removal of the CEL also can be achievedsimultaneously during development of the photoresist under aqueousconditions when a water soluble inert organic binder is used.

STATEMENT OF THE INVENTION

There is provided by the present invention, spin castable contrastenhancement layer (CEL) compositions which comprise, by weight,

(A) 100 parts of solvent,

(B) 1 to 30 parts of inert organic polymer binder, and

(C) 1 to 30 parts of alkylnitrone selected from the class consisting ofarylalkylnitrones and dialkylnitrones.

An additional aspect of the present invention is directed to compositesuseful for making patterned photoresists using mid-UV irradiation,comprising a photoresist and a contrast enhancement layer formed in situthereon, where the contrast enhancement layer is made from a spincastable mixture comprising the above-described spin castable CELcompositions.

A further aspect of the present invention is directed to a method formaking patterned photoresists which comprises,

(A) projecting an aerial image utilizing mid-UV light onto the surfaceof a photoresist having a contrast enhancement layer formed in situthereon,

(B) stripping the resulting photobleached contrast enhancement layerfrom the surface of the photoresist, or simultaneously stripping thephotobleached contrast enhancement layer, and

(C) developing the photoresist layer, where the contrast enhancementlayer is formed by spin casting onto the surface of the photoresist, amixture comprising the above-described spin castable CEL compositions.

Among the arylalkylnitrones which can be utilized in the practice of thepresent invention, there are included compounds such as

α-cinnamyl-N-isopropylnitrone,

α-cinnamyl-N-t-butylnitrone, α-cinnamyl-N-ethylnitrone,

α-phenyl-N-t-butylnitrone, α-anisyl-N-methylnitrone,

α-anisyl-N-t-butylnitrone,

α-(4-diethylaminophenyl)-N-methylnitrone,

α-(4-cyanophenyl)-N-methylnitrone,

α-(4-dimethylaminocinnamyl)-N-methylnitrone,

α-p-tolyl-N-methylnitrone,

α-(3,4-dimethylphenyl)-N-methylnitrone,

α-phenyl-N-methylnitrone, terephthalyl-bismethylnitrone,

α-(4-phenylbutadienyl)-N-methylnitrone,

α-(4-hydroxyphenyl)-N-methylnitrone,

α-furyl-N-methylnitrone, α-furyl-N-isopropylnitrone,

α-(4-quinolinyl)-N-methylnitrone,

α-(2-thiophenyl)-N-methylnitrone,

α-(2-N-methylpyrrolyl)-N-methylnitrone, and

α-(4-methoxycinnamyl)-N-methylnitrone.

Dialkylnitrones which can be utilized in the practice of the presentinvention include bisnitrones derived from glyoxyl andalkylhydroxylamines such as

N,N'-dimethylglyoxalnitrone, N,N'-diethylglyoxalnitrone,

N,N'-di-n-propylglyoxalnitrone,

N,N'-diisopropylglyoxalnitrone,

N,N'-2-(1-hydroxybutyl)glyoxalnitrone, and

N,N'-dicyclohexylglyoxalnitrone.

Inert organic polymer binders which can be utilized in the practice ofthe present invention are polymers such as copolymers of styrene andallyl alcohol, polystyrene, poly(methylmethacrylate),poly(α-methylstyrene), poly(vinylpyrrolidone), polyphenyleneoxide,vinylpyridine/styrene copolymers, acrylonitrile/butadiene copolymers,butylmethacrylic/isobutyl methacrylate copolymers, cellulose propionate,ethyl cellulose, ethylene/vinyl acetate copolymers, polyacenaphthylene,poly(benzylmethacrylate), poly(ethyleneoxide),poly(2-hydroxyethylmethacrylate), poly(4-isopropylstyrene),polyallylalcohol, poly(hydroxypropylmethylcellulose),poly(methylcellulose), and poly(hydroxypropylcellulose).

The term "inert" with respect to the above-shown organic polymer bindersrefers to the ability of the binder to form a photobleachable layer withthe alkylnitrone as previously defined and an in situ CEL on the surfaceof the photoresist which, upon being photobleached, can be readilyremoved from the surface of the photoresist by stripping with a solvent.The stripping of the photobleached CEL can occur as a separate stepprior to developing the photoresist, or it can occur simultaneously withthe development of the photoresist in instances where water solubleinert binder is used as part of an aqueous CEL spin castable mixture. Ininstances where an organic solvent is used in the spin castable CELmixture and stripping prior to development is required, any suitablesolvent can be utilized to effect the removal of the photobleached CELfrom the photoresist. However, it is preferred to utilize an organicsolvent such as toluene, trichloroethylene, chlorobenzene or mixtureswith anisole.

As taught in copending application, Ser. No. 691,829, filed Jan. 16,1985 of P. R. West, for "Photolithographic Stripping Method" which isincorporated herein by reference and assigned to the same assignee asthe present invention, organic solvents can be used to effect theremoval of photobleached CEL derived from spin castable mixturescontaining organic solvent. For example, a mixture of toluene andanisole can be employed as well as stripping with toluene in the form ofa fine mist.

In order that those skilled in the art will be better able to practicethe invention, the following examples are given by way of illustrationand not by way of limitation. All parts are by weight.

EXAMPLE 1

A solution of t-butylhydroxylamine (1.0 g, 11 mmole) and p-anisaldehyde(1.5 g, 11 mmole) in 20 mL of benzene was refluxed through a Dean-Starktrap for 18 hours. One drop of methanesulfonic acid was then added andrefluxing was continued for an additional two hours. The reactionmixture was then washed with saturated aqueous sodium bicarbonate andthe benzene removed under reduced pressure. The residue wasrecrystallized from petroleum ether. Based on the method of preparation,there was obtained 0.8 g (3.9 mmole) or a 35% yield of theα-anisyl-N-t-butylnitrone having a melting point of 90°-1° C.

An ethylbenzene solution was prepared consisting of 8% by weight ofα-cinnamyl-N-t-butylnitrone (synthesized in the same fashion as in theabove example) and 8% by weight of an allyl alcohol/styrene copolymer.The solution was spin-coated at 4000 rpm/25 seconds onto silicon waferscoated with 1.4 micron thick AZ 5214 photoresist. The resulting coatedwafers were printed on a Suss MJB-56 aligner in the UV-300 mode. Theresulting irradiated wafers were stripped by immersion intrichloroethylene for 30 seconds and then were developed with Shipley351 developer utilizing a proportion of 1 part of developer and 5 partsof water. There was resolved 1.5 micron/patterns which were obtainedafter a 36-second exposure. The lines were characterized by havingvertical wall profiles indicating effective contrast enhancement.

EXAMPLE 2

A mixture of 5 g (60 mmole) of methylhydroxylamine hydrochloride and 8 g(61 mmole) of cinnamaldehyde were combined in 25 mL of anhydrousmethanol and stirred for 15 minutes at room temperature. The solvent wasthen removed at reduced pressure and replaced with 50 mL of methylenechloride. The solution was washed with 75 mL of saturated aqueous sodiumbicarbonate followed by washing with a brine solution. After drying overanhydrous magnesium sulfate, the solvent was removed under reducedpressure. The solid residue was titurated with ether, filtered anddried. There was obtained 7.2 g (45 mmole or 74% yield) ofα-cinnamyl-N-methylnitrone having a melting point of 85°-6° C.

A solution of 8% by weight of α-cinnamyl-N-methylnitrone and 8% byweight of an allyl alcohol/styrene copolymer in ethylbenzene wasspin-coated at 4000 rpm for 25 seconds onto silicon wafers coated with1.4 micron-thick AZ5214 resist and a 800A coating of poly vinyl alcohol.The resulting composites were contact printed on a Suss MJB-56 alignerin the UV 300 mode. Vertical wall 1.5 micron lined/spaced patterns wereresolved with a 40 second exposure.

Similar results were obtained with contrast enhancement compositionsutilizing α-cinnamyl-N-isopropylnitrone and α-cinnamyl-N-ethylnitrone.

EXAMPLE 3

A mixture of 7.5 g (100 mmole) of nitroethane, 0.25 g of 9% Pd/C and 80cc of methanol was charged with 50 psi of hydrogen and stirred until 2equivalents of hydrogen were taken up. The reaction mixture whichcontained the ethylhydroxylamine was filtered and to it was added 7.0 g(45 mmole) of 40% aqueous glyoxal. After stirring for 0.5 hours at roomtemperature the methanol was removed under reduced pressure and thesolid residue was triturated with ether. The product was filtered anddried to give 3.44 g (53% yield) of bis-nitrone having a melting pointof 157°-158° C.

A solution of 4% by weight of the ethylglyoxal nitrone and 4% by weightof an allyl alcohol/styrene copolymer in chloroform was spun at 4000 rpmfor 25 seconds onto a quartz disc. The resulting film was exposed to 313nm radiation (about 2.7 mw/cm²) and film transmittance was followed as afunction of time. The initial transmittance of the film was 0% T. Thetransmittance after bleaching was 93% T. This bleaching data isconsistant for a material useful in contrast enhanced photolithography.

EXAMPLE 4

A solution of 4.3% by weight of ethylglyoxal nitrone and 8.7% by weightof a polyvinylalcohol (88% hydrolyzed) in distilled water was spun at3000 rpm for 30 seconds onto a silicon wafer coated with 1.4 micronthick AZ 5214 resist without a barrier coat. The resulting wafer wasprinted on a Suss MJB-56 aligner in the UV-300 mode. The resultingirradiated wafer was then directly developed with Shipley 351 developerutilizing a proportion of 1 part of developer and 5 parts water. Therewas resolved 1.5 micron lined/spaced patterns which were characterizedby having vertical wall profiles indicating effective contrastenhancement.

EXAMPLE 5

A solution of 3.1% by weight of α-cinnamyl-N-isopropylnitrone and 7.5%by weight of a polyvinylalcohol (88% hydrolyzed) in 80/20 by weightwater/methanol was spun onto a silicon wafer coated with 1.4 micronthick AZ 5214 resist without a barrier coat. The resulting wafer wasprinted on a Suss MJB-56 aligner in the UV-300 mode. The irradiatedwafer was then directly developed with Shipley 351 developer as inExample 4. The resulting patterns were characterized by having verticalprofiles indicating effective contrast enhancement.

Although the above examples are directed to only a few of the very manyvariables which can be utilized in the practice of the presentinvention, it should be understood that the present invention isdirected to a much broader variety of arylalkylnitrones,dialkylnitrones, and inert organic polymer binders and the use of suchphotolithographic compositions in water, organic solvent, or mixturesthereof, to treat silicon wafers. Some of the alkylnitrones which can beused in the practice of the invention are shown further by the followingformula: ##STR1## where Z is an organic group selected from the classconsisting of ##STR2## a C.sub.(4-20) aromatic heterocyclic radicalhaving one or more O, N, or S atoms, or a mixture of such heterocyclicatoms, a C.sub.(6-20) aromatic hydrocarbon radical, and a C.sub.(6-20)aromatic hydrocarbon radical substituted with one or more nuclear boundneutral radicals, R, R¹, and R² are monovalent radicals selected fromthe class consisting of hydrogen, C.sub.(1-10) alkyl C.sub.(1-10) alkylsubstituted with neutral radicals, C.sub.(6-20) aromatic hydrocarbon,and C.sub.(6-20) aromatic hydrocarbon substituted with neutral radicals,R³ is a member selected from the class consisting of C.sub.(1-10) alkyland C.sub.(1-10) alkyl substituted with neutral radicals, n is a wholenumber having a value of 0 to 2 inclusive, and m is an integer having avalue of 1 or 2, and when m is 1, Z is monovalent, and when m is 2, Z isdivalent.

What is claimed and sought to be protected by Letters Patent of theUnited States is as follows
 1. A composite useful for making patternedphotoresists using UV irradiation, comprising a photoresist and acontrast enhancement layer formed in situ thereon, where the contrastenhancement layer is made from a spin castable mixture comprising, byweight,(A) 100 parts of solvent, (B) 1 to 30 parts of an inert organicpolymer binder, and (C) 1 to 30 parts of(i) an arylalkylnitrone selectedfrom the group consisting ofα-cinnamyl-N-isopropylnitrone,α-cinnamyl-N-t-butylnitrone, α-cinnamyl-N-ethylnitrone,α-phenyl-N-t-butylnitrone, α-anisyl-N-methylnitrone,α-anisyl-N-t-butylnitrone, α-(4-diethylaminophenyl)-N-methylnitrone,α-(4-cyanophenyl)-N-methylnitrone,α-(4-dimethylaminocinnamyl)-N-methylnitrone, α-p-tolyl-N-methylnitrone,α-(3,4-dimethylphenyl)-N-methylnitrone, α-phenyl-N-methylnitrone,terephthalyl-bismethylnitrone, α-(4-phenylbutadienyl)-N-methylnitrone,α-(4-hydroxyphenyl)-N-methylnitrone, α-furyl-N-methylnitrone,α-furyl-N-isopropylnitrone, α-(4-quinolinyl)-N-methylnitrone,α-(2-thiophenyl)-N-methylnitrone,α-(2-N-methylpyrrolyl)-N-methylnitrone, andα-(4-methoxycinnamyl)-N-methylnitrone, (ii) a dialkylnitrone selectedfrom the group consisting of bisnitrones derived from glyoxyl andalkylhydroxylamines, or (iii) an alkylnitrone of the formula, ##STR3##wherein Z is selected from the group consisting of ##STR4## aC.sub.(4-20) aromatic heterocyclic radical having one or more O, N, or Satoms or a mixture of such heterocyclic atoms, a C.sub.(6-20) aromatichydrocarbon radical, and a C.sub.(6-20) aromatic hydrocarbon radicalsubstituted with one or more nuclear bound neutral radicals, wherein R,R¹, and R² are monovalent radicals selected from the group consisting ofhydrogen, C.sub.(1-10) alkyl, C.sub.(1-10) alkyl substituted withneutral radicals, C.sub.(6-20) aromatic hydrocarbon, and C.sub.(6-20)aromatic hydrocarbon substituted with neutral radicals, wherein R³ isselected from the group consisting of C.sub.(1-10) alkyl andC.sub.(1-10) alkyl substituted with neutral radicals, wherein n is awhole number having a value of 0 to 2 inclusive, and wherein m is aninteger having a value of 1 or 2 with the proviso that, when m is 1, Zis monovalent, and when m is 2, Z is divalent.
 2. The composite of claim1 wherein the dialkylnitrone is selected from the group consistingofN,N'-dimethylglyoxalnitrone, N,N'-diethylglyoxalnitrone,N,N'-di-n-propylglyoxalnitrone, N,N'-diisopropylglyoxalnitrone,N,N'-2-(1-hydroxybutyl)glyoxalnitrone, andN,N'-dicyclohexylglyoxalnitrone.
 3. A method for making patternedphotoresists which comprises,(A) projecting an aerial serial imageutilizing UV light onto the surface of a photoresist having a contrastenhancement layer formed in situ thereon, (B) stripping the resultingphotobleached contrast enhancement layer from the surface of thephotoresist, or simultaneously stripping such photobleached contrastenhancement layer, and (C) developing the photoresist layer, where thecontrast enhancement layer is formed by spin casting onto the surface ofthe photoresist, a mixture comprising, by weight,(1) 100 parts ofsolvent, (2) 1 to 30 parts of inert polymer binder, and (3) 1 to 30parts of (i) an arylalkylnitrone selected from the group consistingofα-cinnamyl-N-isopropylnitrone, α-cinnamyl-N-t-butylnitrone,α-cinnamyl-N-ethylnitrone, α-phenyl-N-t-butylnitrone,α-anisyl-N-methylnitrone, α-anisyl-N-t-butylnitrone,α-(4-diethylaminophenyl)-N-methylnitrone,α-(4-cyanophenyl)-N-methylnitrone,α-(4-dimethylaminocinnamyl)-N-methylnitrone, α-p-tolyl-N-methylnitrone,α-(3,4-dimethylphenyl)-N-methylnitrone, α-phenyl-N-methylnitrone,terephthalyl-bismethylnitrone, α-(4-phenylbutadienyl)-N-methylnitrone,α-(4-hydroxyphenyl)-N-methylnitrone, α-furyl-N-methylnitrone,α-furyl-N-isopropylnitrone, α-(4-quinolinyl)-N-methylnitrone,α-(2-thiophenyl)-N-methylnitrone,α-(2-N-methylpyrrolyl)-N-methylnitrone, andα-(4-methoxycinnamyl)-N-methylnitrone, (ii) a dialkylnitrone selectedfrom the group consisting of bisnitrones derived from glyoxyl andalkylhydroxylamines, or (iii) an alkylnitrone of the formula, ##STR5##wherein Z is selected from the group consisting of ##STR6## aC.sub.(4-20) aromatic heterocyclic radical having one or more O, N, or Satoms or a mixture of such heterocyclic atoms, a C.sub.(6-20) aromatichydrocarbon radical, and a C.sub.(6-20) aromatic hydrocarbon radicalsubstituted with one or more nuclear bound neutral radicals, wherein R,R¹, and R² are monovalent radicals selected from the group consisting ofhydrogen, C.sub.(1-10) alkyl, C.sub.(1-10) alkyl substituted withneutral radicals, C.sub.(6-20) aromatic hydrocarbon, and C.sub.(6-20)aromatic hydrocarbon substituted with neutral radicals, wherein R³ isselected from the group consisting of C.sub.(1-10) alkyl andC.sub.(1-10) alkyl substituted with neutral radicals, wherein n is awhole number having a value of 0 to 2 inclusive, and wherein m is aninteger having a value of 1 or 2 with the proviso that, when m is 1, Zis monovalent, and when m is 2, Z is divalent.
 4. A method in accordancewith claim 3, where an aqueous spin castable mixture is used.
 5. Amethod in accordance with claim 3, where the inert polymer binder iswater soluble.
 6. A method in accordance with claim 3, where the solventin the mixture is an organic solvent.
 7. The method of claim 3 whereinthe dialkylnitrone is selected from the group consistingofN,N'-dimethylglyoxalnitrone, N,N'-diethylglyoxalnitrone,N,N'-di-n-propylglyoxalnitrone, N,N'-diisopropylglyoxalnitrone,N,N'-2-(1-hydroxybutyl)glyoxalnitrone, andN,N'-dicyclohexylglyoxalnitrone.